1. Field of the Invention
The present invention relates generally to light-shielding photosensitive material, and particularly to a method for light-shielding an end portion of photosensitive web material projecting from a light-tight container.
2. Description of the Prior Art
Photosensitive film rolls conventionally have been supplied to film-using apparatus, such as microfilmers, in roll-containing cartridges. The leading end of the outermost convolution of the film roll has been tape-spliced to the trailing end of a flexible opaque leader, which has then been wrapped around the roll, threaded through a cartridge exit slot, folded back, and then taped to the cartridge exterior. The leader, when so applied, has provided both a means for withdrawing the film end from the cartridge and a means for preventing light-piping into the cartridge. However, the added bulk of the film-to-leader splice has sometimes caused the splice to fail when pulled through the constricted exit slot, thereby causing the leader to become separated from the film end and the entire film roll to be lost inside the cartridge. In any event, even when the splice has not failed, and has pulled the film end out of the cartridge, the user has then removed the splicing tape and discarded the leader before threading the film end into the apparatus. For a standard 105 mm-wide (4.133 inches) film roll used with microfilmers, the typical acetate-based leader has been at least 760 mm (30 inches) long. Discarding such a leader in every instance has therefore entailed a significant amount of material waste.
Pertinent in the published prior art is U.S. Pat. No. 4,455,076 to Birkeland, which discloses a daylight-loadable cassette comprising a roll of photosensitive film that is wound upon a flanged spool with its leading end connected to a wider opaque leader, the leader being wrapped around the film in covering relation thereto, with its lateral edges angled radially outwardly and light-tightly against the opposing inward-facing surfaces of the spool flanges to protect the film from ambient light. While the cassette there disclosed may be satisfactory in some applications, it nonetheless poses the same drawbacks described above with reference to use of a spliced leader.
There has thus existed a persistent, long-felt, but unresolved need for a more efficient, reliable, and convenient alternative to the spliced-leader method of enabling film withdrawal from, and preventing light-piping into, a film-roll container.